Hi,

I've been getting poor mileage. People who've read my thread know my gripe. Well, I'm wondering if any of you guys heard of this one: My service manager at Don Beyer Volvo said that my switching between 89 and 93 octane fuel messes up the fuel map in the ECU. He said that a factory rep told him this and that the owners manual even reccomends that an operator stick to one octane rating of fuel. A consequence of a confused fuel map is poor mileage. He said this. The Ecu optimizes engine paramters around multiple variables and fuel octane is one of them.

He was saying that the ECU "learns" the car over multiple driving cycles and runs numbers to compute settings for the most optimal performance. For example, a guy drives a car at say 10-40mph for an extended time period, the ECU incorporates speed variables into its optimization calculations. Accordingly the car is supposed to get its best mileage in that speed range. All of a sudden, start driving 60-70, performance will suck until ECU develops a new performance map. According to what the factory rep told him, the ecu works like the human body's central nervous system. The human body can only regulate irregularities so much before its control mechanisms are overwhelmed. I remember taking a process engineering class in college and we studied controller mechanisms such as thermostats. The Ecu doesn't have an instantaneous optimization response time since it needs to record data that suggests an optimizable performance trend.

Guys, opinions??? Ask around, is this real or bogus? The service manager sounded sincere. Was he trying to razzle dazzle me into shutting up?